Postal workers' leaders warned today that the future of the country's universal delivery system was under threat "as never before" as it raised fresh fears that the service could be privatised.

The Communication Workers Union said it wanted an "honest debate" about the future of the Royal Mail in an attempt to preserve practice of delivering mail anywhere in the UK for the same price.

The union launched its blueprint for a publicly-owned Post Office at Labour's Spring Conference by claiming that the service's reputation had been tarnished by liberalisation. But an official for the Royal Mail said: "The quality of service Royal Mail is delivering is improving."